Ben Affleck and Jennifer Garner are seen at the Democratic National Convention in Denver in 2008.AP

WASHINGTON — Four years ago, Ben Affleck was a familiar presence around the Democratic convention, packing produce for charity and even winning a poker tournament. Singer Fergie performed with her Black Eyed Peas. Sheryl Crow sang, too, with Susan Sarandon joining in from the audience.

But none of these celebrities are planning a similar trip to Charlotte this year, and that’s likely true for a number of other A-listers who were in Denver as well. In terms of star wattage, this gathering will be decidedly less sparkly.

Some reasons are obvious. A re-election bid is hardly as exciting as the historic anointment of the first black nominee, on his way to becoming the first black president. And Barack Obama is no longer a rising star: He’s, well, an incumbent.

Also different is the general tone of this year’s campaign — not so full of lofty thoughts about hope and change, but focused on evoking doubts about Mitt Romney. Romney is trying to do the same with Obama. “This is a campaign based on raising questions about the other candidate,” says Democratic consultant Chris Lehane. “It’s a whole different narrative this time.”

There’s also the possibility that some Hollywood celebrities have lost a measure of their enthusiasm for the candidate they warmly embraced four years ago. The most public of these has been actor Matt Damon, who as recently as last month repeated his disappointment with the president — while adding that he was still the “clear choice.”

At the same time, there’s a sense that the struggling economy, the central preoccupation of most voters, has cast a pall over the celebratory nature of the conventions — and that both campaigns need to be wary of too much partying, with or without celebrities. “Both the Democrats and the Republicans are cognizant of not looking decadent when the rest of the country is hurting,” says Lehane.

Still, it can’t be denied that parties — and if they involve celebrities, as the best ones do, so much the better — are an essential part of conventions. “They’re a natural part of the process,” says Michael Steele, the former RNC chairman. “I don’t think anyone expects the conventioneers to show up in sackcloth. Parties celebrate the grueling process that has gotten us this far. They celebrate the nominee. And they fire up the troops.”

He adds, though, that he expects the parties to be tasteful — “not in-your-face, not ostentatious.”

The Democrats in particular have made a point of saying that this convention has a different mood. They’re spending significantly less than four years ago, they say, and they point out that they’ve limited corporate and special interest money. They also say their parties will have a more public feel.

“Instead of the exclusive, closed-door, party-insider-only events of the past, we’re opening and closing the convention with public events that will allow more people than ever before to participate,” says Democratic National Convention Committee spokeswoman Joanne Peters.

As for the Republicans, “I don’t see any scaling back,” says James Davis, communications director for the Republican National Convention in Tampa. “We’ve got Republicans coming from across the country, some 70-plus venues being booked for events. This is going to be really big for us. I think it shows the excitement of where our party is right now.”

As usual, there will be high-profile entertainment at both conventions. The RNC announced Friday that the Mississippi band 3 Doors Down, Lynyrd Skynyrd and The Oak Ridge Boys would be among the official entertainers in Tampa. The Democrats announced that folk icon James Taylor would perform on the final night in Charlotte, before Obama accepts the nomination.

On the sidelines, the arts advocacy group Creative Coalition will present the band Journey in Tampa — cue the perfect campaign song, “Don’t Stop Believin'” — and the B-52s in Charlotte (cue “Love Shack”?) Given the state of the economy, “I was concerned,” says the coalition’s CEO, Robin Bronk, of the high-profile fundraisers. “But happily we are almost sold out already. This is a celebration of the arts in America.”

And the Recording Industry Association of America is presenting, along with the Auto Alliance of America and others, pop star Gavin DeGraw in Tampa and the rapper Common in Charlotte. Both shows, which will seat some 2,000 people each, benefit the charity Musicians on Call.

“We’re feeling what everyone has been feeling,” says Cara Duckworth, spokeswoman for the RIAA, of the economic concerns. “But this is about celebrating music. We expect to sell out.”

In a way, the relative lack of high-wattage celebrity guests this year may benefit the Democrats. In 2008, the John McCain campaign tried to use Obama’s considerable celebrity appeal against him, most memorably with an ad likening him to Britney Spears and Paris Hilton: i.e. all splash and no substance. Earlier this year, the pro-GOP super PAC American Crossroads put out an ad asking: “After 4 years of a celebrity president is your life any better?”

Obama’s campaign did try to downplay celebrity presence in Denver, keeping it on the sidelines. But still, luminaries of the entertainment world — from Spike Lee to Anne Hathaway to Obama’s biggest booster, Oprah Winfrey — were there in droves.

The AP called representatives of a number of celebrities who were in Denver to ask if they were coming this year. Of those who responded, all said no, except for Jessica Alba: The actress will be headlining a final-night party with her husband, Cash Warren, featuring performances by Pitbull and Scissor Sisters.

Also, Eva Longoria, a co-chair of Obama’s campaign, will be speaking at the convention.

Traditionally there have been fewer celebrities at Republican conventions. Two past attendees are skipping Tampa, though, according to their representatives: former California Gov. Arnold Schwarzenegger, now back in show business, and actor Robert Downey Jr., who was at the last GOP convention, but also attended an Obama fundraiser in May at George Clooney’s home.

Speaking of Clooney, many powerful Hollywood boosters of Obama simply prefer to stay away from conventions but maintain their strong support nonetheless. Like Clooney, Sarah Jessica Parker and movie mogul Harvey Weinstein, all of whom have hosted major fundraisers recently, some obviously feel they can be of greater use in other ways than hanging out in Charlotte.

And the most important thing is what happens after the convention, says Steele, who notes he worked hard when he was RNC chairman to create relationships with celebrities.

“Of course, the real goal is to have these stars then go out on the road for you in the fall,” Steele says.